Ultra-wideband Luneburg lens with high performance based on gradient metamaterials
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Abstract Based on the perspective of a wide scanning range and ultra-broad bandwidth, Luneburg lenses are highly anticipated to be an outstanding option for multibeam radiation. However, owing to the lack of low-loss continuously varying permittivity materials, the practical application of Luneburg lenses is far below the expected level. In this paper, an ultra-wideband planar Luneburg lens (PLL) is proposed. Due to the novel design of an all dielectric lightweight radially symmetric periodic gradient metamaterial, the presented lens is able to yield highly directional emission with side lobes all below −8 dB and achromatic sub-diffraction focusing with full width at half maximum about 0.4 λ from 4 GHz to 22 GHz. The prototype of the lens is manufactured by computer-numerical controlled machining. The measured data of the near field and far field agree well with that of the simulated data, verifying the effectiveness of the proposed design methodology. The superiority of the presented approach to design a Luneburg lens is demonstrated. Therefore, the PLL has the advantages of being lightweight, with a compact structure, low profile, ultrabroadband function, high resolution, and convenient fabrication, giving it great potential to be practically deployed.Keywords:
Luneburg lens
Wideband
Achromatic lens
A Luneburg lens is described which has been fabricated from foam glass. The electrical performance is presented at X-band. The theoretical power-handling capability of this lens is conservatively estimated at 6 times that of an equivalent lens fabricated from expanded polystyrene.
Luneburg lens
Polystyrene
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We present the design, fabrication, and experimental characterization of a modified two-dimensional Luneburg lens based on bulk metamaterials. The lens is composed by a number of concentric layers. By varying the geometric dimensions of unit cells in each layer, the gradient refractive index profile required for the modified Luneburg lens can be achieved. The cylindrical waves generated from a point source at the focus point of the lens could be transformed into plane waves as desired in the microwave frequency. The proposed modified Luneburg lens can realize wide-angle beam scanning when the source moves along the circumferential direction inside the lens. Numerical and experimental results validate the performance of the modified Luneberg lens.
Luneburg lens
Simple lens
Gradient-index optics
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Various aspects of implementing a gradient refractive index distribution using 3D printing are considered. These approaches are applied to two types of lens design: cylindrical Luneburg lens and thick flat lens. Based on simulated and measured results the main constraints for the lens design using additive manufacturing are defined. The novelty of the work consists of the study of the influence of different approaches to the implementation of lenses using additive technologies on the characteristics of the antenna. The approaches for a lens measured as a Luneburg lens and a thick flat lens are compared.
Luneburg lens
Gradient-index optics
Three dimensional printing
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This paper details the design of a printed-circuit-board implementation of a 2D Luneburg lens. The refractive index of the lens is controlled through a combination of meandering crossed microstrip lines and varying their widths. The 12.4lambda o diameter lens is designed to operate in the Transverse Electromagnetic (TEM) mode at 13 GHz. The lens was designed, fabricated, and measured. The measured half power beamwidth of the experimental lens is 5.26deg.
Luneburg lens
Beamwidth
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Abstract In this work a design of 250 mm F/20 lens for hyperspectral imaging of biomedical micro objects is presented. The designed lens consists of only standard optical elements and does not contain any newly developed component. Its low aperture and small field of view causes that image quality is limited only by diffraction and two optical aberrations – field curvature and chromatic focal shift. That is why an achromatic doublet is utilized as a basic lens component. Its residual field curvature is corrected by a Smith lens – a single plane-concave lens located near the image plane. The components are selected from commercially available ones. A distance between components was the only optimized parameter. Such layout makes the lens cheap and easy to manufacture.
Achromatic lens
Simple lens
Chromatic aberration
Aperture (computer memory)
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Based on conformal mapping method, a two dimensional, multi-functional lens structure is proposed and designed in this work. The lens is an infinitely-long, gradient-index dielectric cylinder with a semi-elliptic cross-section. The lens can first be considered like a flattened Luneburg lens, which produces highly-directive electromagnetic waves by adjusting the feed position along the line connecting the two foci. It also functions like an Eaton lens. When an incoming beam impinges on the same line but outside the two foci, it will be guided through the lens structure and take a U-turn. Besides, if properly shaped, the structure can also be used as a waveguide bend. The lens can be realized using non-resonant metamaterials with inhomogeneous hole arrays. Simulation results demonstrate excellent performance of the lens and agree well with theoretical prediction. The designed lens can be used in the electromagnetic control. And it is especially useful in the real optical lens system.
Luneburg lens
Gradient-index optics
Simple lens
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A zoned fishnet metamaterial lens is designed, fabricated, and experimentally demonstrated at millimeter wavelengths to work as a negative near-zero refractive index lens suitable for compact lens antenna configurations. At the design frequency f = 56.7 GHz (λ0 = 5.29 mm), the zoned fishnet metamaterial lens, designed to have a focal length FL = 9λ0, exhibits a refractive index n = −0.25. The focusing performance of the diffractive optical element is briefly compared with that of a non-zoned fishnet metamaterial lens and an isotropic homogeneous zoned lens made of a material with the same refractive index. Experimental and numerically-computed radiation diagrams of the fabricated zoned lens are presented and compared in detail with that of a simulated non-zoned lens. Simulation and experimental results are in good agreement, demonstrating an enhancement generated by the zoned lens of 10.7 dB, corresponding to a gain of 12.26 dB. Moreover, beam steering capability of the structure by shifting the feeder on the xz-plane is demonstrated.
Beam steering
Metamaterial antenna
Luneburg lens
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Applying the directionality of an acoustic meta-lens, a sound reception system for ships is designed. A two-dimensional disk shape acoustic meta-lens or an acoustic Luneburg lens made of 253 acrylic pipes of different radii which control the refractive index is used. The lens has the diameter of 180 cm and the thickness of 20 cm. Eight microphones were installed around the edges of the lens because the lens focuses the input signal into the edge of the other side of the lens. The sound reception ability of the lens was tested on the sea using the horn of a university training ship as an emitter and the lens loaded on a small boat as a receiver. Both are moving at 20 ~ 40 km/h at a distance between 300 ~ 700 m. The lens could focus to recognize the direction of the input sound in the frequency range between 300 and 900 Hz.ABBREVIATIONS IMO: International Maritime Organization ALL: Acoustic Luneburg Lens SRS: Sound Reception System
Luneburg lens
SIGNAL (programming language)
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Various materials, lens structures, and processes are examined relative to the lens requirements of an RF spectrum-analyzer implemented through the use of an integrated-optics format. Factors which distinguish optical-waveguide lenses and reflectors from conventional imaging lens systems are enumerated. It is concluded that a thin-film Luneburg lens is the most viable planar approach based upon the use of oxides and, when high refractive-index materials must be employed, the spherical depressed geodesic becomes a feasible alternate.
Luneburg lens
Gradient-index optics
Waveguide
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Citations (55)